Various types of seat belt and airbag systems have been used to protect passengers in automobiles, aircraft and other vehicles. In automobiles, airbags typically deploy from the steering column, dashboard, side panel, and/or other fixed location. During a rapid deceleration event (e.g., a collision), a sensor detects the event and transmits a corresponding signal to an initiation device (e.g., a pyrotechnic device) on an airbag inflator. Initiation causes the inflator to release compressed gas into the airbag via a hose, thereby rapidly inflating the airbag. There are a number of different types of inflators known in the art. Some inflators contain compressed gas (e.g., air, nitrogen, helium, argon, etc.). Other inflators (e.g., gas generating devices) provide high pressure gas via chemical reaction of an energetic propellant.
Airbags can be deployed in a number of positions around the vehicle passenger or driver. Airbags positioned in the steering column, for example, can inflate in front of the driver to cushion his head and torso from forward impact. Airbags can also reduce the likelihood of whiplash.
Although airbags that deploy from stationary locations (e.g., a steering column) may be effective in automobiles, they may not be as effective in other types of vehicles having other seating arrangements. Seats in commercial passenger aircraft, for example, can be configured in a variety of layouts that provide different spacing between succeeding rows and adjacent seats. Moreover, such layouts may lack the availability of stationary structures upon which to mount airbags. Additionally, seatbacks in aircraft may rotate forward and downward during a crash or similar event, and thus may be unsuitable for airbag storage. As a result, airbags have been developed that deploy from seatbelts to accommodate occupants in aircraft and other vehicles. Such airbags can deploy from, for example, a lap belt and/or a shoulder belt to provide additional protection during a crash or other rapid deceleration event. Such airbag systems are described in detail in U.S. Pat. No. 5,984,350, which is owned by the assignee of the present application and is incorporated herein in its entirety by reference.
Seatbelt airbag systems generally utilize electronic activation systems and circuitry to facilitate or enhance their protective features. It is generally desirable in such systems to ensure that the airbag does not inadvertently inflate when it is not needed, such as when a person is not present in the associated seat. At the same time, of course, systems designed to prevent inadvertent inflation should not prevent inflation when the seat is occupied and inflation is desired. For these reasons, various types of airbag activation systems have been developed that include means for determining whether a seatbelt connector and corresponding buckle have been engaged (i.e., to determine the “buckle status”), and thereby determine whether or not the seat is occupied. One such system utilizes a “normally open” reed switch in cooperation with a magnet. In general, the reed switch is mounted to the connector on one portion of the seatbelt, and the magnet is mounted to the buckle on the other portion of the seat belt. When the connector and the buckle are joined together to buckle the seatbelt, the magnet closes the reed switch. Closing the reed switch closes a corresponding electrical circuit that enables power to be provided for airbag initiation in the event of a crash.